A nimbostratus is a thick, dark gray cloud that brings steady rain or snow for hours at a time. When you wake up and see the whole sky covered in a flat, gloomy blanket of clouds with rain falling steadily, you're looking at nimbostratus clouds.

Unlike thunderstorm clouds that tower up dramatically and dump heavy rain in a short burst, nimbostratus clouds spread across the sky in layers and produce that gentle, persistent rain that makes you grab an umbrella before school. They sit relatively low in the atmosphere, low enough that their bottoms can look ragged and blurry.

These clouds form when warm, moist air slowly rises and spreads out, creating that uniform gray covering that can last all day. Meteorologists consider nimbostratus one of the main cloud types that brings precipitation. If you see one overhead, you know you're in for a long, rainy stretch rather than a quick shower.